Strain insulator



Dec. 7, 1943. P. L. WARREN STRAIN INSULATOR Filed Oct. 50. 1941 152062725/ ficieffln arrea Patented Dec. 7, 1943 STRAIN IN SULATOR Pickett L. Warren,

Chicago, 111., assignor to Royal Electric Manufacturing Company, Chicago, Ill., a corporation of Illinois Application October 30, 1941, Serial No. 417,070

4 Claims.

This invention relates to strain insulators and more particularly to such strain insulators as are used for insulating a guy wire that guys a wooden power line supporting pole.

Power transmission lines of low voltage and of medium or even high voltages are frequently supported by wooden oles. These poles, or certain of them, must be held by guy wires to counteract the pull of the power line or lines, as is well known in the art. Where a guy wire extends from adjacent the top of the pole to the ground it reduces the effective line to ground insulation, losing the insulating value of the wood pole. It is therefore necessary to interpose an insulator in series with the guy Wire, between the grounded end of the wire and the end that is connected to the pole. This insulator, in one well known. form of construction, consists of a wooden rod one end of which is connected to the part of the guy wire that is secured to the top of the pole, and the opposite end of which is connected to the part of the guy wire that is anchored in the ground. The guy wire is tightened to be under great tension, thus placing the wooden rod under great tension. Suitable bolts pass through the ends of the wooden insulator structure to secure it to the guy wires. Since each securing bolt is of comparatively small diameter it exerts a comparatively high pressure against the wood at the pe riphery of the hole through which the bolt extends. It is one of the objects of the present invention to provide means for reducing the stress in the wooden rod around or adjacent the bolts. This is accomplished, in the preferred embodiment of the present invention, by two comparatively large metal'rings embedded in the wood concentric with the hole through which the rod extends but very much larger than that hole, so that the metal rings increase the effective area from which the stress of the securing bolt is transmitted to the wood. The two rings are of a combined length appreciably less than the thickness of the rod, preferably of a combined length of the order of half the thickness of the block. As a result the rings do not appreciably reduce the strength of the block in tension and do inhibit any tendency for the bolts to sheer through the wood.

In the preferred embodiment of the present invention the wooden strain insulator is provided with arcing horns at opposite ends thereof to bypass any are that might otherwise tend to jump through the insulator. These arcing horns are secured to the ends of the insulator by the same bolts that also secure the guy wires to the insulator.

The attainment of the above and further objects of the present invention will be apparent from the following specification taken in conjunction with the accompanying drawing forming a part thereof.

In the drawing:

Figure 1 is a view of a pole of a medium voltage power tansmission line, illustrating the use of a guy wire strain insulator embodying the present invention;

Figure 2 is a longitudinal view of the strain insulator of Figure 1;

Figure 3 is a view, in partial section, taken at right angles to Figure 2;

Figure 4 is an enlarged sectional view through the end of the strain insulator of Figure 3; and

Figure 5 is a sectional view taken along the line 55 of Figure 4.

Reference may now be had more particularly to the drawing Where in like reference numerals indicate like parts throughout.

In the drawing I is a wooden pole of a medium high voltage power transmission line, said pole being embeddded in the ground and supporting at its upper end a cross arm 2 on which are supported petticoat type insulators 33 each of which in turn supports a power conductor or line 4 as is usual in transmission lines of this type. The pole is braced by guys 5-5 one end of which is connected to the upper end of the pole and the opposite end of which is anchored in the ground. Each guy includes a strain insulator 8, and a wire 9. The wire 9 is secured to one end of the insulator 8, the opposite end of the insulator being connected to the pole l by another wire. The wire 9 is under tension thus placing the strain insulator under tension. The strain insulator includes a pair of arcing horns ill-16. The strain insulator is interposed between the pole and the grounded wire 9 to increase the amount of insulation between the power line 4 and ground. In the absence of an insulator 8 the guy wire would bring the ground potential up to the top of the pole thus losing the insulating value of the wooden pole I.

Reference may now be had more particularly to Figures 2 through 5 showing the construction of the strain insulator 8. The strain insulator includes a wooden oar l2 preferably, although not necessarily, of clear fir wood rectangular in cross section, the two ends of which are of identical construction so that a description of the metal construction at one end will suffice also for that of the other end. A clevis I5 consisting of two similar iron straps Iii-I6 is secured to the end of the bar I2, as by a pair of bolts l'll8 that extend through the straps I6 and are tightened in place by a lock nut l9 and a split Washer 20. The shank of each bolt extends through a hole 2! in the bar l2. Open ended circular metal rings 24-25 are embedded in the wooden bar l2 surrounding and concentric with the hole 2|. Each ring 24 is of an internal diameter approximately twice the diameter of the bolt hole 2|. Each ring is of an axial length of the order of onequarter to one-eighth of the thickness of the bar l2 so that the combined lengths of the two rings 24-25 is approximately one-quarter to one-half of the thickness of the wooden bar I2, although these figures are given for illustrative purposes only. The same bolts I'|--|8 that secure the straps I6-l6 to the bar l2 also secure the arcing horn Hi to the strain insulator inelectrical contact with one of the straps I6.

A thimble Si is mounted between the ends of the straps l6-I5 by a pin 3| held in place by a cotter pin 32. The thirnble provides a sheath for the end of the guy wire, which guy wire is looped around the grooved thimble 30 and then the end of the guy wire is secured to the rest of the wire in the manner known in the art. The guy wire is thus electrically connected to the arcing horn Iii.

It is apparent that the guy wire exerts a tension on the strain insulator l2. This tension is transmitted from the guy wire to the two straps iii-l6 and the bolts Ill8 to the strain insulator. The bolts exert a pressure upon the wood of the insulator. Since the bolt is of a small cross sectional area the unit pressure of the bolt against the wood may be appreciable. By interposing the rings 24-25, which are of much larger diameter than the bolt, the effective area against which the pressure of the bolt is exerted upon the wood is thus increased. By making the rings 24-45 discontinuous the tensile strength of the wood fibers between the two rings is retained.

In compliance with the requirements of the patent statutes I have here shown and described a preferred embodiment of my invention. It is, however, to be understood that the invention is not limited to the precise construction here shown, the same being merely illustrative of the principles of the invention. What I consider new and desire to secure by Letters Patent 1. A strain insulator connected in series with a tensioned conducting guy wire extending between ground and an insulating electric line pole to interpose insulation between the grounded guy wire and the pole, said insulator comprising a rod of wood, a pair of metallic straps at opposite sides of the red at one end thereof, a connection between the straps and the guy wire and a connection between the straps and the rod, said last mentioned connection including a bolt passing through the straps and the rod and a metallic ring embedded in the rod concentrically with the bolt and of an internal diameter substantially greater than the diameter of the bolt receiving hole in the rod, the wood of the rod extending into the ring, and the ring terminating flush with one surface of the rod of wood and in conductive relation to the associated strap whereby the ring and the associated bolt are maintained at the same potential, and means at the opposite surface of the rod of wood for reducing the electric stress between the bolt and the wood adjacent said opposite surface.

2. A strain insulator connected in series with a tensioned conducting guy wire extending between ground and an insulating electric line pole to interpose insulation between the grounded guy wire and the pole, said insulator comprising a rod of wood, a pair of metallic straps at opposite sides of the rod at one end thereof, a connection between the straps and the guy wire and a connection between the straps and the rod, said last mentioned connection including a bolt passing through the straps and the rod and metal rings embedded in the rod concentrically with the bolt and each of an internal diameter substantially greater than the diameter of the boltreceiving hole in the rod, and each ring terminating flush with the surface of the rod of wood and in conductive relation to the straps whereby the rings and the associated bolt are maintained at the same potential.

3. A strain insulator for connection in series with a member exerting a pull on the insulator, said insulator comprising a bar of wood having a bolt hole therethrough for receiving a bolt to secure the insulator to the member, said insulator having a pair of metallic rings embedded therein from opposite sides thereof and each ring surrounding the hole and the wood extending into the ring and of substantially greater internal diameter than the diameter of the surrounded hole, each of said rings terminating substantially flush with the outer surface of the bar of wood and penetrating the bar to less than half the thickness of the bar.

4. A strain insulator connected in series with a tensioned conducting guy wire extending from an insulating electric line pole, said insulator comprising a wood rod, a bolt hole extending through the wood insulator at the end thereof, a pair of metal rings each of an internal diameter substantially greater than the diameter of the bolt hole, said rings being each of a length substantially less than half of the thickness of the wooden rod at the bolt hole and being embedded respectively in opposite sides of the rod concentric with the bolt hole and terminating substantially flush with the outer surfaces of the wooden rod, apair of metallic straps overlying opposite sides of the rod at the end thereof and overlying the ends of the rings and extending beyond the end of the rod, a bolt extending through the bolt hole and through the straps for securing the straps to the wood insulator, the wood of the rod filling the space between the bolt and the rings, a connection between the extended ends of the straps and the guy wire, and an arcing horn secured in electric conductive relationship to the straps by said bolt, the bolt and the rings being both in electric conductive relationship to the straps whereby the surfaces of wood in contact with thebolt and with the rings are maintained at the same electric potential.

PICKETT L. WARREN.

CERTIFICATE OF CORRECTION. Patent No. 2, 556,52 L. December 7, 1915. PICKETT L. WARREN.

It is hereby certified thrit error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2",; second column, lines 514 and 55, claim 3, after "hole" strike out"and the wood extending into the ring and insert the same after "hole" and before the coma in line 57, same claim; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. I

Signed and sealed this 1st day of February, A, D. 19%.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION. Patent No. 2, 356521;. December 7, 1915.

PICKETT L. WARREN.

It is herein; certified tht error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2",; sec- 0nd column, lines 514. and55, claim 5, after "hole" strike out*'and the wood extending into the ring" .and insert the same after "hole" and before the comma in line 57, same claim; and that the said Letters Patent should be read with fiais correction therein that the same may conform to the record of the case in thePatent Office. I

Signed and sealed this 1st day of February, A, D. 191 1;.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents. 

